An effective gametocide is a chemical compound that, when applied to a plant during sexual development, is capable of sterilizing a plant's male gametes while leaving the plant's female gametes, or at least a significant proportion of them, capable of undergoing cross fertilization with subsequent high yields of fertile, viable hybrid seed.
The utility of a gametocide lies in the area of plant hybridization. By causing pollination of one variety of a plant species by a different variety of the same species, a hybrid plant is obtained. By careful selection of the parents, hybrids can be obtained with specific combinations of desirable traits such as plant size, grain yield, disease resistance, herbicide tolerance and climatic adaptation.
Hybridization utilizing cytoplasmic male sterility is available and is used to produce commercial hybrid corn and wheat seed. However, using such techniques, it can take years to develop lines to the point that commercial quantities of hybrid seed are produced. The use of an effective gametocide significantly reduces this development time.
Some plants, such as corn, can be easily hybridized without resort to the use of gametocides because the organ containing the male gametes are exposed and can easily be removed. This leaves the female gametes available for cross-fertilization.
However, this is not true with plants which are self-pollinating by nature such as wheat. The male and female wheat gametes are found inside the same flower which remains closed until the male anthers release their pollen onto the female gametes to fertilize them. Thus, when the flower opens, fertilization is normally complete. For a gametocide to be useful on wheat it must sterilize the male gametes and avoid interfering with the opening of the flower when the female gametes are ready for fertilization.
Substituted pyridones and pyridazines are known in the art as gametocides as disclosed in U.S. Pat. Nos. 4,115,101 and 4,345,934.
However, there still is a need in the art for a more effective gametocide which effectively sterilizes the male gametes while leaving the female gametes capable of undergoing cross fertilization with a subsequent high yield of fertile viable hybrid seed.